1. Field of Endeavor
The present invention relates to microfluidics and more particularly to a magnetohydrodynamic (MHD) pump.
2. State of Technology
Background information is contained in U.S. Pat. No. 5,876,187 for micropumps with fixed valves to Fred K. Forster et al., patented Mar. 2, 1999 including the following: “Miniature pumps, hereafter referred to as micropumps, can be constructed using fabrication techniques adapted from those applied to integrated circuits. Such fabrication techniques are often referred to as micromachining. Micropumps are in great demand for environmental, biomedical, medical, biotechnical, printing, analytical instrumentation, and miniature cooling applications. Just as in larger applications, various pump designs are required for different micropump systems. The valve components of micropumps may include passive polysilicon check valves, gas-controlled valves with silicon membranes, solenoid-actuated valves with nickel diaphragms, and magnetically or electrostatically driven control valves. Valves that include components that are actuated or otherwise driven can be characterized as active valves. Manufacture and operation of active valves can add substantial complexity and cost to the production of micropumps. Passive-type valves, such as those having movable polysilicon check valves, can be manufactured with reduced complexity, although these valves can fail when the pumped fluid includes particulates. In this regard, the particulate sizes are of the same order of magnitude as the passages in the micropumps. The passive valves become obstructed by particulates and are, therefore, unable to provide a sufficient seal when required. As a result, such valves have limited effectiveness when employed for pumping fluids that include particulates. Similarly, active valves that employ substantially rigid sealing membranes or diaphragms are susceptible to seal failure when used to pump fluids containing particulates. The particulates become embedded in the sealing surface as a result of the relatively high pressure applied to the rigid diaphragm as needed to ensure a seal with such a valve. Once the particulates become embedded in the sealing surface, the valve is thereafter prevented from fully closing. Fixed valves are valves having no moving parts. Fixed valves represent the utmost simplicity and high reliability for pumping fluids. Such valves, which do not include parts that periodically seal and move apart, are especially advantageous for micropump systems used for pumping fluids that include particulates. Moreover, fixed-valve pumps are particularly useful for biological applications that require pumping fluids that contain cells. The cells are not damaged by the fixed valve pumps, as would otherwise occur in moving-parts valves. The effectiveness of fixed valves can be characterized by the parameter “diodicity,” which is the ratio of pressure drop in the reverse-direction fluid flow through the valve to the pressure drop in the forward-direction fluid flow through the valve, for a given flow rate. A basic design consideration for a fixed valve micropump is to develop valve configurations that result in a diodicity greater than 1.0. In this regard, the small size of such valves, and the very low flow range (100 nl/min to 50 ml/min, for example) will typically yield a relatively low Reynolds number, which number is a dimensionless parameter that is proportional to the product of the valve size and flow velocity. Accordingly, the valve configurations must effect the requisite diodicity in flows characterized by low Reynolds numbers, where flow separation and turbulence (with attendant significant pressure losses) are unlikely to occur. U.S. Pat. No. 1,329,559 discloses a fixed valve that is designated as a “valvular conduit.” The conduit is provided with enlargements, recesses, and projections that are said to offer virtually no resistance to the passage of fluids in one direction, yet provide a nearly impassible barrier to fluid flow in the opposite direction. When an oscillating flow of fluid is applied to one end of the conduit, the conduit acts as a one-way valve or fluidic diode, thereby permitting the oscillated or pulsed fluid to be pumped through the conduit. The conduit is mounted to a piston that is rapidly reciprocated to provide the pulsed flow of fluid through the conduit. The valvular conduit described in U.S. Pat. No. 1,329,559 is full-sized, constructed of metal, and used for delivering fluids with flows that can most likely be characterized as having a relatively high Reynolds number. No insight is provided in that patent as to how such a conduit could be adapted to a micropump system and flows characterized by low Reynolds numbers.”
Background information is contained in U.S. Pat. No. 6,146,103 for micromachined magnetohydrodynamic actuators and sensors to Abraham P. Lee and Asuncion V. Lemoff, patented Nov. 14, 2000 including the following: “Microfluidics is the field for manipulating fluid samples and reagents in minute quantities, such as in micromachined channels, to enable hand-held bioinstrumentation and diagnostic tools with quicker process speeds. The ultimate goal is to integrate pumping, valving, mixing, reaction, and detection on a chip for biotechnological, chemical, environmental, and health care applications. Most micropumps developed thus far have been complicated, both in fabrication and design, and often are difficult to reduce in size, negating many integrated fluidic applications. Most pumps have a moving component to indirectly pump the fluid, generating pulsatile flow instead of continuous flow. With moving parts involved, dead volume is often a serious problem, causing cross-contamination in biological sensitive processes. The present invention utilizes MHDs for microfluid propulsion and fluid sensing, the microfabrication methods for such a pump, and the integration of multiple pumps for a microfluidic system. MHDs is the application of Lorentz force law on fluids to propel or pump fluids. Under the Lorentz force law, charged particles moving in a uniform magnetic field feel a force perpendicular to both the motion and the magnetic field. It has thus been recognized that in the microscale, the MHD forces are substantial for propulsion of fluids through microchannels as actuators, such as a micropump, micromixer, or microvalve, or as sensors, such as a microflow meter, or viscosity meter. This advantageous scaling phenomenon also lends itself to micromachining by integrating microchannels with micro-electrodes.” The disclosure of U.S. Pat. No. 6,146,103 is incorporated herein by reference.